Fluid machine

ABSTRACT

A fluid machine including a shaft and an impeller, wherein the impeller has a shaft bore into which the shaft is inserted, and wherein the impeller is coupled to the shaft by an interference fit. The fluid machine further includes a positioning part provided between the shaft and the impeller, for positioning the impeller at a predetermined position on the shaft; a fitting part provided inside the shaft bore and adjacent to the positioning part, for forming the interference fit between the shaft and the impeller; and a loose-insertion part provided inside the shaft bore and adjacent to the fitting part, for forming a clearance between the shaft and the impeller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to fluid machinery and, moreparticularly, to a fluid machine including a shaft and an impellercoupled to each other by an interference fit.

2. Description of the Related Art

In a fluid machine of a high-speed rotation type, such as a blower usedin a laser oscillator, it is required to firmly or fixedly attach animpeller to a shaft (or a rotary shaft) with high positional accuracy.To this end, conventionally, the impeller is fitted to the shaft by ashrinkage fit, so as to prevent a relative positional deviation in acircumferential direction of the impeller and the shaft, which may occurduring the high-speed rotation thereof, and to allow them to rotatestably at high speed, as described in, e.g., Japanese Unexamined PatentPublication (Kokai) No. 7-063193 (JP-A-7-063193).

Further, there is known a configuration in which the impeller is fitted,at only a part of a shaft bore thereof, to the shaft by the shrinkagefit, as described in Japanese Unexamined Patent Publication 2004-060460(JP-A-2004-060460). JP-A-2004-060460 also describes a technique in whichthe impeller is mounted on a surface plate with the gas-intake side ofthe impeller being directed upward and, in this state, a fitting partprovided at the gas-intake side in the shaft bore of the impeller issubjected to heat to increase the inner diameter of the fitting partand, after the shaft is inserted downward into the shaft bore up to apredetermined position from an upper side of the impeller, the heat isremoved to complete the shrinkage fit.

In a conventional fluid machine in which the impeller is fitted to theshaft by the shrinkage fit, a relative fixing position between theimpeller and the shaft is typically determined based on a point at whichthe impeller is first engaged with the shaft during the shrinkage of theimpeller and, thereafter, the impeller completely shrinks to be firmlyfixed to the shaft. In this connection, it is generally difficult toaccurately estimate the fixing position of the impeller on the shaft(i.e., the position of the first engagement point) due to, e.g., unevenmachining accuracy of the impeller and the shaft. Therefore, it isdifficult to accurately locate and fix the impeller at a predeterminedposition in an axial direction on the shaft and, as a result, theoperational reliability and/or performance of the fluid machine may beadversely affected.

For example, in a configuration in which a shaft seal and/or a bearingare mounted adjacent to the impeller, if the axial position of theimpeller on the shaft is deviated from a set position, the axialpositions of the shaft seal and the bearing are also deviated from setpositions thereof accordingly. In particular, if the positionaldeviation of the bearing is caused, abnormal vibration may occur andthus the bearing or the body of the fluid machine may be damaged duringthe high-speed rotation of the shaft. This problem may arise not only inthe configuration in which the impeller is fixed to the shaft at theentire length of the shaft bore, as described in JP-A-7-063193, but alsoin the configuration in which the impeller is fixed to the shaft at apart of the shaft bore, as described in JP-A-2004-060460, because of thefact that the fixing position of the impeller on the shaft (i.e., theposition of the first engagement point) is difficult to specify.

In order to solve the above problem, it is known that, in the shrinkagefit process, the impeller and the shaft are securely bound or held by,e.g., a press machine, to prevent the relative positional deviation inthe axial direction therebetween, until the impeller shrinks completely.Further, it is known that, for the sake of reducing a time spent for thecomplete shrinkage of the impeller, a cooling mechanism for an exclusiveuse is provided. However, these subsidiary apparatuses, such as thepress machine, the cooling mechanism and the like, may result inincrease in the manufacturing costs of the fluid machine.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fluid machineincluding a shaft and an impeller, coupled to each other by aninterference fit, wherein it is possible to surely prevent, by a simplestructure, a relative positional deviation in an axial direction causedbetween the shaft and the impeller during a coupling work thereof, andthereby to ensure an inexpensive and high-performance configuration withan excellent safety and operational reliability.

To accomplish the above object, the present invention provides a fluidmachine comprising a shaft; an impeller having a shaft bore into whichthe shaft is inserted, the impeller being coupled to the shaft by aninterference fit; a positioning part provided between the shaft and theimpeller, for positioning the impeller at a predetermined position onthe shaft; a fitting part provided inside the shaft bore and adjacent tothe positioning part, for forming the interference fit between the shaftand the impeller; and a loose-insertion part provided inside the shaftbore and adjacent to the fitting part, for forming a clearance betweenthe shaft and the impeller.

In the above-described fluid machine, the positioning part may comprisea member separated from the shaft and the impeller.

Also, the positioning part may comprise a part of at least one of theshaft and the impeller.

Also, the fitting part and the loose-insertion part may be formed byvarying, along an axial lengthwise direction, at least one of an outerdiameter of the shaft and an inner diameter of the shaft bore of theimpeller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments in connection with the accompanying drawings,wherein:

FIG. 1 is a sectional view showing a shaft and an impeller of a fluidmachine according to an embodiment of the present invention;

FIG. 2 is a sectional view showing a modification of the fluid machineof FIG. 1;

FIG. 3 is a sectional view showing another modification of the fluidmachine of FIG. 1;

FIG. 4 is a sectional view showing a further modification of the fluidmachine of FIG. 1; and

FIG. 5 is a sectional view showing an yet further modification of thefluid machine of FIG. 1.

DETAILED DESCRIPTION

The embodiments of the present invention are described below, and indetail, with reference to the accompanying drawings. In the drawings,the same or similar components are denoted by common reference numerals.

Referring to the drawings, FIG. 1 shows a shaft 12 and an impeller 14 ofa fluid machine 10 according to an embodiment of the present invention.The fluid machine 10 according to the illustrated embodiment isconfigured as a centrifugal blower, and a known blade structure of theimpeller 14 and a known structure of a housing (not shown) can be usedfor the fluid machine 10, the descriptions of which are thus omitted. Itshould be noted that the present invention can be applied not only tothe centrifugal blower but also to other various fluid machines.

The fluid machine 10 includes a shaft 12 and an impeller 14 having ashaft bore 16 into which the shaft 12 is inserted, and is configured sothat the impeller 14 is coupled to the shaft 12 through an interferencefit. The fluid machine 10 further includes a positioning part 18provided between the shaft 12 and the impeller 14, for positioning theimpeller 14 at a predetermined position on the shaft 12; a fitting part20 provided inside the shaft bore 16 and adjacent to the positioningpart 18, for forming the interference fit between the shaft 12 and theimpeller 14; and a loose-insertion part 22 provided inside the shaftbore 16 and adjacent to the fitting part 20, for forming a clearancebetween the shaft 12 and the impeller 14.

The shaft 12 is provided with a stepped cylindrical outercircumferential surface 12 a extending along the rotation axis A of theshaft 12 and impeller 14 with the outer diameter of the outercircumferential surface 12 a varying in a stepped manner. The impeller14 is coaxially fixed to the outer circumferential surface 12 a of theimpeller 14 at the predetermined axial position of the outercircumferential surface 12 a. The shaft bore 16 of the impeller 14 has acylindrical inner circumferential surface 16 a extending along therotation axis A of the shaft 12 and the impeller 14 with the innerdiameter of the inner circumferential surface 16 a being kept constant.The shaft 12, to which the impeller 14 is fixed, is rotatably supportedby the housing (not shown) through a bearing 24 attached to the shaft 12at its predetermined axial position. A shaft seal 26 is securely mountedto the shaft 12 at a predetermined axial position between the impeller14 and the bearing 24.

The outer circumferential surface 12 a of the shaft 12 includes acylindrical large-diameter portion 28, on which the bearing 24 and theshaft seal 26 are mounted; a cylindrical intermediate-diameter portion30 disposed axially adjacent to the large-diameter portion 28, thediameter of which is slightly reduced in comparison with thelarge-diameter portion 28 through a first annular-shoulder surface 12 bgenerally orthogonal to the rotation axis A; and a cylindricalsmall-diameter portion 32 disposed axially adjacent to theintermediate-diameter portion 30, the diameter of which is slightlyreduced in comparison with the intermediate-diameter portion 30 througha second annular-shoulder surface 12 c generally orthogonal to therotation axis A. The shaft seal 26 includes a cylindrical base 34adapted to be fitted to the large-diameter portion 28 of the shaft 12.The base 34 of the shaft seal 26 is disposed to be aligned, at one axialend (an upper end, in the drawing) thereof, with the firstannular-shoulder surface 12 b of the shaft 12, and is disposed to beadjacent, at the other end (a lower end, in the drawing) thereof, to thebearing 24. The impeller 14 is fixed to the intermediate-diameterportion 30 of the shaft 12 at a first region 36 of the innercircumferential surface 16 a of the shaft bore 16, which extends over apredetermined length from one axial end (a lower end, in the drawing) ofthe inner circumferential surface 16 a. A remaining region (or a secondregion) 38 of the inner circumferential surface 16 a of the shaft bore16 of the impeller 14 is disposed so as not to contact thesmall-diameter portion 32 of the shaft 12.

In the illustrated embodiment, the positioning part 18 is configuredfrom the first annular-shoulder surface 12 b of the shaft 12 and thebase 34 of the shaft seal 26, the base 34 being a member separated fromboth of the shaft 12 and the impeller 14. The impeller 14 receives thesmall-diameter portion 32 and the intermediate-diameter portion 30 ofthe shaft 12 successively in this order from one axial end (a lower end,in the drawing) of the shaft bore 16, and is abutted, at an annular area14 a of an axial end face adjacent to an opening at one axial end of theshaft bore 16, against both of the first annular-shoulder surface 12 bof the shaft 12 and one axial end face (an upper end face, in thedrawing) of the base 34 of the shaft seal 26. In this state, theimpeller 14 is accurately located at the predetermined axial position onthe shaft 12.

Further, in the illustrated embodiment, the fitting part 20 isconfigured by the cooperation between the intermediate-diameter portion30 of the outer circumferential surface 12 a of the shaft 12 and thefirst region 36 of the inner circumferential surface 16 a of the shaftbore 16. The interference-fit configuration in the fitting part 20 canbe surely obtained by at least one (or both) of processes of “ashrinkage fit” in which the impeller 14 is heated to be attached to theshaft 12 and “an expansion or cooling fit” in which the shaft 12 iscooled to be attached to the impeller 14. The outer diameter of theintermediate-diameter portion 30 of the shaft 12 and the inner diameterof the first region 36 of the shaft bore 16 are determined so as toensure an interference sufficient to achieve an interference-fitstructure having a desired strength. Also, the axial length of theintermediate-diameter portion 30 of the shaft 12 is determined so as tobe sufficient to eliminate an inclination of the axis of the impeller 14relative to the shaft 12. Still further, in the illustrated embodiment,the loose-insertion part 22 is configured by the cooperation between thesmall-diameter portion 32 of the outer circumferential surface 12 a ofthe shaft 12 and the second region 38 of the inner circumferentialsurface 16 a of the shaft bore 16.

In the fluid machine 10 configured as described above, when the shaft 12is fixed to the impeller 14 by at least one of the shrinkage fit processand the expansion fit process, the small-diameter portion 32 and theintermediate-diameter portion 30 of the shaft 12 are first insertedsuccessively in this order into the shaft bore 16 of the impeller 14,and the annular area 14 a of the axial end face of the impeller 14 isbrought into abutment with the positioning part 18 (i.e., the firstannular-shoulder surface 12 b of the shaft 12 and the base 34 of theshaft seal 26), whereby it is possible to accurately locate the impeller14 at the predetermined axial position on the shaft 12. Then, the shaft12 and the impeller 14 are left standing in this state, so that theimpeller 14 as heated can shrink in the case of the shrinkage fit, oralternatively the shaft 12 as cooled can expand in the case of theexpansion fit, and thereby the shaft 12 and the impeller 14 are engagedwith each other first in the fitting part 20 (i.e., theintermediate-diameter portion 30 of the shaft 12 and the first region 36of the shaft bore 16). During this step, due to the weight of theimpeller 14 or a slight external force, the state where the annular area14 a of the impeller 14 abuts against the positioning part 18 can beeasily maintained and, therefore, the shaft 12 and the impeller 14 areengaged with each other first at a certain point in the fitting part 20in the state where the impeller 14 is surely located at thepredetermined axial position on the shaft 12.

Thereafter, heat is exchanged between the shaft 12 and the impeller 14that are in contact with each other and, thereby, the expansion of theshaft 12 and the shrinkage of the impeller 14 are substantiallysimultaneously performed, so that the interference fit in the fittingpart 20 is completed. The subsequent expansion of the shaft 12 and thesubsequent shrinkage of the impeller 14, after the completion of theinterference fit, advance in directions reverse to each other, as shownby arrows in FIG. 1. Such thermal deformations of both the shaft 12 andthe impeller 14 in the reverse directions can be smoothly performed, dueto the provision of the loose-insertion part 22 (i.e., thesmall-diameter portion 32 of the shaft 12 and the second region 38 ofthe shaft bore 16). Then, at an instant when the thermal deformations ofboth the shaft 12 and the impeller 14 are finished, the operation forattaching the impeller 14 to the shaft 12 is completed. The impeller 14thus attached to the shaft 12 possesses a significantly high positionalaccuracy in the axial direction.

As described above, in the fluid machine 10 in which the fitting part 20is provided adjacent to the positioning part 18 inside the shaft bore16, it is possible, when the shaft 12 is fixed to the impeller 14 by atleast one of the processes of the shrinkage fit and the expansion fit,to easily and surely specify the fixing position of the impeller 14 onthe shaft 12 (i.e., the position of the first engagement point) and thusto establish the interference fit in the fitting part 20. Further, theloose-insertion part 22 is provided adjacent to the fitting part 20inside the shaft bore 16, so that it is possible to control theexpansion of the shaft 12 and the shrink of the impeller 14, after thecompletion of the interference fit, in the predetermined directions. Asa result, it is possible to surely prevent, by a simple structure, arelative positional deviation in an axial direction caused between theshaft 12 and the impeller 14 during the coupling work thereof, so as toimprove the positional accuracy in the axial direction of the impeller14 on the shaft 12, as well as of the other components attached to theshaft 12, such as the bearing 24, the shaft seal 26 and the like.Accordingly, the fluid machine 10 can ensure an inexpensive andhigh-performance configuration with an excellent safety and operationalreliability.

It should be noted that, in the above-described configuration in whichthe interference fit between the shaft 12 and the impeller 14 is ensuredby at least one of the processes of the shrinkage fit and the expansionfit, it is advantageous that the shaft 12 and the impeller 14 are madeof materials having mutually different heat-shrinkage rates, in view offacilitating the effect of the interference fit.

In the fluid machine 10 described above, the positioning part 18 mayalso be configured by either one of the base 34 of the shaft seal 26(i.e., a member separated from the shaft 12 and impeller 14) and thefirst annular-shoulder surface 12 b of the shaft 12 (i.e., a part of theshaft 12). In the case where the positioning part 18 is configured byusing a component provided for other purposes, such as the shaft seal 26attached to the shaft 12 and adjacent to the impeller 14, it is possibleto reduce the number of manufacturing steps and the number ofcomponents. On the other hand, in the case where the positioning part 18is configured by a part of at least one of the shaft 12 and the impeller14, it is possible to maintain the stable positioning function.

Further, the fitting part 20 and the loose-insertion part 22 may bedefined by varying, along an axial lengthwise direction, a diametraldimension of at least one of the outer circumferential surface 12 a ofthe shaft 12 and the inner circumferential surface 16 a of the shaftbore 16 of the impeller 14. According to this configuration, the fittingpart 20 and the loose-insertion part 22 can be configured very simplyand easily. Hereinafter, various modifications of the above-describedfluid machine 10 will be described with reference to FIGS. 2 to 5. Thecomponents shown in FIGS. 2 to 5, corresponding to those of the fluidmachine 10 in FIG. 1, are designated by common reference numerals, andthe descriptions thereof are not repeated.

In a modification shown in FIG. 2, in place of the above-describedintermediate-diameter portion 30, the shaft 12 is provided, at the outercircumferential surface 12 a thereof, with a tapered portion 40 definedbetween the first annular-shoulder surface 12 b and the small-diameterportion 32, the outer diameter of the tapered portion 40 being graduallyreduced starting from the first annular-shoulder surface 12 b up to thesmall-diameter portion 32. The tapered portion 40 is engaged, at a pointadjacent to the first annular-shoulder surface 12 b, with an end portion36 a of the above-described first region 36 in an interference-fitcondition, the end portion 36 a being adjacent to the opening end (thelower end, in the drawing) of the shaft bore 16 of the impeller 14,opening to the positioning part 18, and thereby the fitting part 20 isconstituted. In this configuration, provided that a sufficientinterference is obtained for the interference fit in the fitting part20, it is possible to establish a fitting structure having a requiredstrength, and also to eliminate the inclination of the axis of theimpeller 14 relative to the shaft 12 by the function of the positioningpart 18 (i.e., the first annular-shoulder surface 12 b of the shaft 12and the base 34 of the shaft seal 26). According to this configuration,characteristic effects, equivalent to those of the fluid machine 10shown in FIG. 1, are also ensured.

In a modification shown in FIG. 3, the intermediate-diameter portion 30and the second annular-shoulder surface 12 c, as described above, areeliminated from the outer circumferential surface 12 a of the shaft 12,so that the large-diameter portion 28 and the small-diameter portion 32are adjacent to each other with the first annular-shoulder surface 12 barranged therebetween. On the other hand, the inner circumferentialsurface 16 a of the shaft bore 16 of the impeller 14 is formed to have astepped cylindrical shape including the above-described first region 36defined by a small-diameter cylindrical surface and the above-describedsecond region 38 defined by a cylindrical surface having a diameterlarger than the first region 36. The first region 36 of the shaft bore16 of the impeller 14 is engaged with a distal end area 42 of thesmall-diameter portion 32 of the shaft 12 in an interference-fitcondition, the distal end area 42 being adjacent to the firstannular-shoulder surface 12 b, and thereby the fitting part 20 isconstituted. In this configuration, provided that a sufficientinterference and a sufficient axial length are obtained for theinterference fit in the fitting part 20, it is possible to establish afitting structure having a required strength, and also to eliminate theinclination of the axis of the impeller 14 relative to the shaft 12.According to this configuration, characteristic effects, equivalent tothose of the fluid machine 10 shown in FIG. 1, are also ensured.

In a modification shown in FIG. 4, the outer circumferential surface 12a of the shaft 12 is formed so that the large-diameter portion 28 andthe small-diameter portion 32 are adjacent to each other with the firstannular-shoulder surface 12 b arranged therebetween, in a manner similarto the configuration of FIG. 3. On the other hand, the shaft bore 16 ofthe impeller 14 is provided in the inner circumferential surface 16 athereof with the above-described second region 38 defined by alarge-diameter cylindrical surface and a tapered region 44 definedbetween the second region 38 and the opening end (the lower end, in thedrawing) opening to the positioning part 18, the inner diameter of thetapered region 44 being gradually reduced starting from the secondregion 38 up to the opening end. The tapered region 44 of the shaft bore16 is engaged, at a point adjacent to the opening end opening to thepositioning part 18, with an end portion 32 a of the small-diameterportion 32 of the shaft 12 in an interference-fit condition, the endportion 32 a being adjacent to the first annular-shoulder surface 12 b,and thereby the fitting part 20 is constituted. In this configuration,provided that a sufficient interference is obtained for the interferencefit in the fitting part 20, it is possible to establish a fittingstructure having a required strength, and also to eliminate theinclination of the axis of the impeller 14 relative to the shaft 12 bythe function of the positioning part 18 (i.e., the firstannular-shoulder surface 12 b of the shaft 12 and the base 34 of theshaft seal 26). According to this configuration, characteristic effects,equivalent to those of the fluid machine 10 shown in FIG. 1, are alsoensured.

In a modification shown in FIG. 5, in place of the above-describedpositioning part 18 using the shaft seal 26, a positioning part 46formed by parts of both the shaft 12 and the impeller 14 is providedinside the shaft bore 16 of the impeller 14. More specifically, theouter circumferential surface 12 a of the shaft 12 is formed so that thelarge-diameter portion 28 and the small-diameter portion 32 are adjacentto each other with the first annular-shoulder surface 12 b arrangedtherebetween, and that the large-diameter portion 28 is extended toprotrude from the base 34 of the shaft seal 26 and inserted into theshaft bore 16 of the impeller 14. On the other hand, the innercircumferential surface 16 a of the shaft bore 16 of the impeller 14 isformed to have a stepped cylindrical shape including the large-diameterfirst region 36 adjacent to the opening end (the lower end, in thedrawing) opening to the shaft seal 26, the large-diameter second region38 adjacent to the opposite opening end, and a small-diameter thirdregion 48 defined between the first region 36 and the second region 38.Also, in the shaft bore 16 of the impeller 14, an annular-shouldersurface 16 b substantially orthogonal to the axis A is formed betweenthe first region 36 and the third region 48. The annular-shouldersurface 16 b of the shaft bore 16 of the impeller 14 cooperates with thefirst annular-shoulder surface 12 b of the shaft 12 and, thereby, thepositioning part 46 is constituted. Further, the third region 48 of theshaft bore 16 of the impeller 14 is engaged with a distal end area 50 ofthe small-diameter portion 32 of the shaft 12 in an interference-fitcondition, the distal end area 42 being adjacent to the firstannular-shoulder surface 12 b and, thereby, the fitting part 20 isconstituted.

In the above configuration, when the shaft 12 is fixed to the impeller14 by at least one of the shrinkage fit process and the expansion fitprocess, the small-diameter portion 32 and the large-diameter portion 28of the shaft 12 are first inserted successively in this order into theshaft bore 16 of the impeller 14, and the first annular-shoulder surface12 b of the shaft 12 is brought into abutment with the annular-shouldersurface 16 b of the shaft bore 16 of the impeller 14, whereby it ispossible to accurately locate the impeller 14 at the predetermined axialposition on the shaft 12 by the function of the positioning part 46. Inthis state, the interference fit is completed in the fitting part 20(i.e., the distal end area 50 of the small-diameter portion 32 of theshaft 12 and the third region 48 of the shaft bore 16), so that it ispossible to attach the impeller 14 to the shaft 12 in the state wherethe impeller 14 is accurately located at the predetermined axialposition on the shaft 12. During a period when heat is exchanged betweenthe shaft 12 and the impeller 14, that are in contact with each other atthe fitting part 20, the thermal deformations of the shaft 12 and theimpeller 14 advance in the directions shown by arrows in FIG. 5.According to this configuration, as the positioning part 46 and thefitting part 20 are provided adjacent to each other inside the shaftbore 16, it is also possible to easily and surely specify the fixingposition of the impeller 14 on the shaft 12 (i.e., the position of thefirst engagement point) and thus to establish the interference fit inthe fitting part 20. As a result, characteristic effects, equivalent tothose of the fluid machine 10 shown in FIG. 1, are also ensured.

While the invention has been described with reference to specificpreferred embodiments, it will be understood, by those skilled in theart, that various changes and modifications may be made thereto withoutdeparting from the scope of the following claims.

1. A fluid machine comprising: a shaft; an impeller having a shaft boreinto which said shaft is inserted, said impeller being coupled to saidshaft by an interference fit; a positioning part provided between saidshaft and said impeller, for positioning said impeller at apredetermined position on said shaft; a fitting part provided insidesaid shaft bore and adjacent to said positioning part, for forming saidinterference fit between said shaft and said impeller; and aloose-insertion part provided inside said shaft bore and adjacent tosaid fitting part, for forming a clearance between said shaft and saidimpeller.
 2. A fluid machine as set forth in claim 1, wherein saidpositioning part comprises a member separated from said shaft and saidimpeller.
 3. A fluid machine as set forth in claim 1, wherein saidpositioning part comprises a part of at least one of said shaft and saidimpeller.
 4. A fluid machine as set forth in claim 1, wherein saidfitting part and said loose-insertion part are formed by varying, alongan axial lengthwise direction, at least one of an outer diameter of saidshaft and an inner diameter of said shaft bore of said impeller.